Best post yet! I too approach checking out a bass from a different perspective. The very first thing I do is check to see how the neck profile feels in my hand. If it doesn't have that fit, I go no further. If it does seem like it could be there, I will play it unplugged for a few minutes. If after that time it still appeals to me, I leave it alone, and come back at least a few days later at an odd hr when the store is most likely at it's quietest. Again I pick up the bass, and if it doesn't immediately feel there, I walk. If it does, I repeat the first process again.This time however, I play every note on the bass (still unplugged) slowly and deliberately to check the loudness and uniformity of the notes, as well as listen for dead spots. If a bass sounds good unplugged, it will sound usually as good plugged in. Only after it passes that test, will I bother plugging it in to see if it has that magic. This may seem like a waste of time to many, but I am NOT going to the store to audition. I am going to look at a possible instrument to purchase.
As mentioned by someone earlier, when checking out an amp, I usually play very little. Instead I ask a sales person to play my bass as well as one in the store of his choosing. I really am not interested in his/her ability, but rather their willingness to help play what I ask as I set and change gain, eq, etc. A really young salesman at GC helped me one night for almost an hr playing for me as I checked out a LMII. He played whole notes, sustained notes, finger style, slap, walking, and even some chords for me, all on my asking. I could not have been more appreciative for his help. After my session with him, I purchased the amp without even playing one note through it myself. I found out all I needed to by being able to tweak the amp and listen with both hands free while the bass was being played, and having the ability to walk around and listen to the eq changes I had made. Again, I did NOT go there to audition, I went there to buy an amp.
A funny story comes to mind. Back in the 90's I went to a musicians flea mkt and rented a space to sell some items. I had one real nice piece to sell. It was a vintage MM Stingray ash/maple in mint shape. I swear to you at least a hundred people played that bass that day. 99 of them played some wanky slap crap that made me want to puke. One older gentleman sat down and played some wonderful melodic lines for about five minutes. Guess who bought it?